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If you watch somebody cooking pasta, you’ll almost always see them adding some salt to the water. When you ask why, they’ll say they add the salt either to improve the flavour, or to make the water boil at a higher temperature so that the pasta cooks faster.

When you add heat to water, you turn the liquid water into steam. The steam expands, and in doing so, has to push against the surrounding atmosphere. That’s why water doesn’t always boil at 100° C.

At high altitudes the atmospheric pressure is low, so water will boil at a lower temperature. In the Himalayas, I saw our porters bring the water to the boil, and add spaghetti – but it never fully cooked. We were about 12,000 feet (3,658 metres) above sea level.

At that altitude, the boiling point of water is only 88° C. No matter how long they boiled the water, it would never get hotter than 88° C, and so the pasta was always a little crunchy.

The opposite situation happens inside a pressure cooker. The pressure is significantly higher than atmospheric pressure, so the water won’t boil until it gets to 120° C. This higher temperature really speeds up the cooking.

The claim is that adding salt to water does the same. It increases the temperature at which the water boils, which then supposedly cooks the pasta more quickly.

Now water is a very common, but very unusual, liquid. It has kept the physicists and chemists guessing for the last century-and-a-half. That’s a big achievement for such a simple chemical, which has only two atoms of hydrogen married to just one atom of oxygen.

First, compare H 2O to other similar liquids. The easy way to do this is to use the Periodic Table of The Elements, and look at the elements that are similar to oxygen, and then marry them to hydrogen. These chemicals turn out to be H 2S, H 2Se, H 2Te. These chemicals have very low boiling points, but H 2O bucks the trend. You would predict (from the graph) that its boiling point would be -50° C – instead, +100° C. That’s 150 C° higher than expected.

The second weird thing about water, is that as you cool it, it becomes more dense (which you would expect) until it hits 4° C. Then it becomes less dense. This very unusual behaviour is still not explained.

And third, we still don’t fully understand how water boils. The water molecule is shaped like a microscopic right-angled boomerang. There’s a negatively charged oxygen atom in the middle of the "V", and two positively charged hydrogen atoms, one on each end of the boomerang’s arms.

In regular water, the H 2O molecules jostle around until the positive charge of one molecule attracts the negative charge of another. As you heat up the water, you put more energy into the system and these positive-negative attraction bonds start breaking.

Surprisingly, it seems that as these attraction bonds break, that they create a microscopic cavity completely empty of water molecules. Smaller cavities merge to make bigger cavities, which in turn somehow lead to molecules of water breaking free into the atmosphere. Yes folks, we’ve reached boiling point.

And yes, adding salt to water changes things. In pure water, the water molecules are all fairly organized. When you throw in some salt, its molecules can wander around almost at random. These extra molecules increase the disorder, and this "magically" increases the temperature at which the water boils. (If you want to know more, look up any Second Year Physics textbook on Phase Equilibria and the Clausius-Clapeyron equation.)

So yes, salt increases the boiling temperature, but not by very much. If you add 20 grams of salt to five litres of water, instead of boiling at 100° C, it’ll boil at 100.04° C.

So a big spoon of salt in a pot of water will increase the boiling point by four hundredths of a degree! So adding salt to water will not cook your pasta faster – unless your watch is calibrated in microseconds.

If you are in that much of a hurry, you should run with your pasta to the dining table, not walk. Just be happy with the knowledge that salt does improve the flavour.